1. Field of the Invention
This invention relates to an improved process for the low temperature carbonization of residues produced by the hydrogenation of oil, especially heavy oil, or of coal. More specifically, these residues, produced during the hydrogenation process, are subjected to low temperature carbonization in a drum, preferably a rotary drum, at temperatures between 400.degree. C. and 600.degree. C., whereby a carbonization gas is introduced, after the separation of the condensable portions and heating to temperatures between 600.degree. C. and 950.degree. C., into the low temperature carbonization drum and the low temperature carbonization of the residues is thereby effected.
2. Description of the Prior Art
In the hydrogenation of coal and mineral oils, especially of distillation residues of mineral oils as well as of heavy and very heavy oils at temperatures of 400.degree. C.-520.degree. C. and pressures of 100-700 bars in the liquid phase, the hydrogenation product contains, in addition to the desired products that are volatile at the reaction temperature, nonvolatile residues, such as asphaltenes, catalysts and unreacted carbon in coal hydrogenation and/or coal or coke as catalyst supports in oil hydrogenation. The residues are separated from the gaseous product in one or more hot separators and must be reprocessed. In the coal hydrogenation process used in Germany until the end of World War II, residues, optionally after increasing the solids content by centrifuging, were introduced into a low temperature carbonization plant, in which nonvolatile portions were decomposed into gas, oil and coke.
A typical low temperature carbonization plant for the hydrogenation residues consisted of a slightly inclined rotary drum type kiln externally heated by gas burners, into which the pasty residue, preheated to 400.degree. C.-450.degree. C., was introduced and subjected to low temperature carbonization at temperatures of approximately 550.degree. C.-600.degree. C. (cf. W. Kroenig "Die katalytische Druckhydrierung von Kohlen, Teeren und Mineraloelen," Berlin/Goettingen/Heidelberg 1950, especially pages 44-45 and 188-189 as well as M. Hoering and E. E. Donath in "Ullmanns Enzyklopaedie der technischen Chemie," third edition, volume 10, Munich/Berlin 1958, especially pages 518-519.) To avoid coke deposits building up on the inside of the walls of the drum, the latter contained steel balls that removed deposits from the walls as the drum revolved by attrition. About 100 kg of steam per ton of feedstock were introduced into the drum to act as a sweep-through gas.
In this previous and known process, the specific throughput of the low temperature carbonization drum was essentially determined by the heat introduced from the outside per square meter of drum surface. By preheating the residue to be carbonized to a temperature as close as possible to the cracking temperature, the heated drum surface could be correspondingly reduced or the drum throughput increased. However, this method of increasing throughput was limited by the onset of the cracking reaction during the heating period, if the preheating temperature became too high.
Since the contents of the low temperature carbonization drums were heated externally, through the walls of the drums, this process required a great deal of energy and therefore was not very economical. Moreover, the annoyance caused by the noise of the steel balls falling inside the drum was considerable. Furthermore, purification of the foul water resulting from condensation of the sweep-through steam was very expensive. Therefore, it was generally believed that such low temperature carbonization drums or processes would not be used in the future (cf. Winnacker-Kuechler, "Chemische Technologie," Munich/Vienna 1981, Volume 5, page 457).